Electrolytic detinning



Och 1953 F. A. LOWENHEIM ELECTROLYTIC DETINNING Filed July 20, 1948 CIRCTIiLNmTING ff 79 Q 0 Q 30 //0 0 0 0 0 0 500 0 L 0 0 0 oo8o 0%0 o O O o 00 0 5 0 0 08 O O O SPENT CATHOLYTE $8952;

IN VEN TOR. eaer/cfi 4..

BY Lowe/M A 7' TORA/EYJ Patented Oct. 13, 1953 2,655,473 UNITED STATES PATENT OFFICE 2,655,473 ELECTROLYTIC DETINNING Frederick A. Lowenheim, Plainfield, N. J., assignor to Metal & Thermit Corporation, New

ork, N. Y., a corporation of New Jersey Application July 20, 1948, Serial N 39,727 3 Claims. (Cl. 204-121) having a rotatable scrap drum or container and is taken at right angles to the axis of rotation of the scrap drum, a portion of the drum being broken away;

scrap. The invention particularly relates to a 5 Fig. 2 is a section along the line 2-2 of Fig. 1;

which is broken away; and

Fig. 4 is a flow diagram of a detinning process to detin the scrap. employing a modified detinning apparatus.

lar er size than is ordinarily possible in conv n- An anode in the form of a circular plate [8, having perforations I9, is provided at the bottom of the tank and is supported therein by non-conducting or insulated supports 20, 20', 2|, and 2|.

cathode Which are mainta n d n the bath Out Of from opposite sides thereof. Any source of direct contact means a e e m te n the Operation the extend for some distance into the bath solution cathode.

th portion of it djacent the anode being 40 operating practice. The position of the cathodes cathodic, and the portion adjacent the cathode being anodic. Oxygen gas is generated from the which is so pos ti ned in h Pa Of the Oxygen the sides 01 the scrap drum in order to permit in the form oi sodium stannate, which 'Z to wheel-shapedsupports 32 and 33 secured adjacent 35 is attached to the supports 32, 33. The shaft trated and in which:

Fig. 1 is a v r ical section or a plating vessel to reducer 43.

3 Scrap 44, such as tin plate clippings and the like, is loosely packed in the form of variously sized fragments and pieces in drum 30 and may be continuously or intermittently moved or agitated in the bath through rotation of the drum.

is to the cathodes 25, 26, the scrap acts as a bipolar electrode. According to the principle of bipolar electrodes, although the scrap is not directly connected in the electric circuit, it yet serves to conduct current. This is because the resistance to the current offered by the scrap is less solution intermediate the anode and the cathodes, and hence at least some current will tend to flow through the scrap. That portion of the scrap which the current enters after leaving the solution is cathodic, in accordance with familiar electrochemical principles, and that portion of the scrap which the current leaves to enter the solution is anodic. Consequently, the scrap nearest the anode l8 acts like a cathode andthat nearest the cathodes 25, 26 acts like an anode- Since the tin with which the scrap is plated is soluble in the bath, it will dissolve from the anodic portion of the scrap and will be plated out of the solution upon the cathodes 25, 26.

As indicated above, the bath comprises an aqueous solution of caustic alkali, such as sodium hydroxide and/or potassium hydroxide, and such alkali may vary in concentration from about 1% to as high a concentration as that in which sodium stannate is substantially soluble. A preferred concentration range is about 3 to about 20% for sodium hydroxide and about 1 to about 40% for potassium hydroxide, with a concentration of about 5% for either material being specially useful. sodium hydroxide, being less expensive, is the preferred alkali. Some, but not all, of these alkalis may be replaced by a carbonate such as sodium or potassium carbonate. The bath may be operated over a wide range of temperatures, say from room temperature to boiling, with temperatures above 60 C. being preferred. Operating time will depend on various factors, such as the size of the scrap charge, current density, etc., although in practice a period of from about 1 to about 5 hours is generally employed. The curren its choice depends chiefly on economic factors. The voltage, however, should be at least high enough to decompose water, or about 2.7 volts. The upper limit of the voltage may vary widely. The anode should be insoluble in the bath. Steel is the preferred material, although other materials which do not dissolve in the caustic alkali solution are useful, such as nickel, nickelplated iron, cobalt, cobalt-plated iron, iron plated with nickel and cobalt, platinum and other noble metals, graphite, silver, and iron alloys such as duriron, stainless steel, etc. The cathode may be any suitable metal, the most common metals being iron or tin. Any variety of tin plate scrap 'is suitable for detinning.

The tin deposit obtained on the cathode as a result of detinning has good adherent properties and may be melted directly off the cathode. It is to be distinguished overthe spongy tin produced by some conventional electrolytic detinning processes which must be scraped, rather than melted, off the cathode. It is fusible, has a good color and a metallic appearance. It may be melted and cast directly, without smelting, in distinction again over spongy tin, which must be smelted before use.

During passage of the current from the anode The operation of the bath is quite simple. Impurities introduced thereto along with the scrap, some of which are converted to sodium soaps, maybe removed through line 15 and valve l1. When necessary, the bath may be replenished by adding water and caustic alkali in suitable proportions.

Following are some examples illustrating the operation of the above described method and apparatus.

Detin- 1 I Curnmg Run 233 Grams Hours rentefL, Volts s analypercent sis, per- I cent tin In all of the runs, relatively small pieces of crumpled scrap were placed in a basket and immersed in a 5% aqueous caustic soda solution.

In the table, the column headed Grams, tin represents the calculated amount of tin on the tin plate scrap. The column headed Detinning analysis, percent tin represents the analysis of the detinned scrap and shows the amount of tin left on the detinned scrap. All of the runs show that detinning may be completed in about 2 to about 3 hours. In all cases a current of 2.5 amperes was used.

In runs 4 and 5 the basket containing the scrap was turned from top to bottom halfway through the run, since it was noted that that part of the scrap nearest the bath cathode tended to be detinned first. Turning or rotating the scrap thus had the effect of speeding up the detinning of that part of the scrap which was originally more remote from the bath cathode.

Runs 1 and 2 are interesting in that in run 1 the electrical connections were reversed so that the bath anode was above the scrap. The effect of anodic oxygen on the scrap was thus eliminated and only bipolar detinning was operative. In run 2 the bath anode was below the scrap and hence anodic oxygen was able to impinge upon the scrap. According to run 2, it is indicated that oxygen detinning is beneficial since only 0.07% tin was left on the detinned scrap, which is satisfactory. The amount of tin left on the detinned scrap in run 1, 0.21%, is very unsatisfactory for commercial requirements.

In run 3 the bath anode was placed to one side of the bath and the cathode on the other side so that the oxygen generated at the anode merely bubbled up the side of the anode without impinging on the scrap. Accordingly, in this run only the bipolar effect occurred. The scrap basket was turned in this run. Run 3 may be compared with run 5; in the former, despite the fact that less scrap was present, the detinning was much less effective for the same time than in run 5, in which a greater amount of scrap was used. Also, the cathode deposit in run 5 was superior to that of run 3.

In a modification of the above described method and apparatus, the cathodes may be surrounded with means such as a porous wall or diaphragm of microporous rubber or other suitable material, which will allow ions to pass through but not coarser or gross material. The diaphragm thus tends to keep the solution in the cathode vicinity or compartment, i. e. the catholyte, from mechanically mixing with the solu- 2,655,478 6 tion in the anode vicinity or compartment, 1. e. In the light of the foregoing description, the the anolyte. The anolyte can then be withfollowing is claimed: drawn from the plating tank and impurities such 1. Apparatus for recovering tin from tin plate be continuously replaced by the enriched anothe container, said anode being insulatedly lyte, and the spent catholyte, which comprises mounted in said vessel in a substantially horicaustic alkali solution, can at the same time be 10 zontal position with respect to said container, a

anode compartment, purifying it, and returning and from the container and scrap, said scrap beit to the cathode compartment, and for transing thus positionable intermediate the anode and ferring the catholyte to the anode compartment cathode so as to intercept anodic oxygen generatare provided Such a modified method and aped at the anode and to function as a bipolar elecscribed. Drum 50 is rotatable in the manner 2. Method for detinning tin scrap and recoverscrap to the cathodes 56, 57 disposed in cathode electric current through the bath from the anode compartment 58. The latter surrounds the upper to the cathode and intermediately through the rent leaves the cathodes through conductor 60. mate contact with the scrap to aid in dissolving such as lead, zinc, arsenic, antimony iron etc 3. Method for recovering tin from tin scrap and it is then withdrawn from tank 5| via line which comprises suspending the scrap m a bath BI and valve 62 by means of pump 63 and deof aqueous caustic alkali solution having an mlivered throu h line 64 to treating tank 65 which soluble anode disposed below the scrap and a may comprise one or a series of stages The 1mcathode above the scrap, passing an electric ourother treatment. For example, lead a d zinc cathode and intermediately through the solution line 7| to the cathode compartment 58. Spent the cathode, plating the tin content of said latter ment 75 of the detinning tank. anolyte solution removed therefrom.

According to the modification of Fig. 4, the FREDERICK A. LOWENHEIM.

scrap in anode compartment 15 may be detinned by anodic oxygen and the current, while in the References clted m the file of @1118 Patent cathode compartment 58 latconditignetd or puri- 60 UNIT D T E P T fied solution is being dep e ed of i s in After the tin concentration of the anolyte has reached gg g ggg g a1 f a certain level, and its free alkali concentration 907061 Leitch Dec 1908 in turn has decreased, it is removed, purified, and 1 511967 Holland 1924 sent to the cathode compartment to give up its 1983296 Lacher f {1934 tin content and be regenerated with respect to 2'196355 Cremer 1940 alkali. In other Words, the catholyte consists of j j Vonmer 1940 mate? t 2,243,165 Mandi May 27, 19 While the invention has been described and 2 350 669 Boner June 6 1944 illustrated by reference to more or less specific embodiments, it will be understood that the prin- FOREIGN PATENTS ciples of the invention are capable of variation Number Country Date within the scope thereof. 327,997 Great Britain Apr. 15, 1930 

1. APPARATUS FOR RECOVERING TIN FROM TIN PLATE SCRAP COMPRISING A VESSEL FOR SOLUTION, A ROTATABLE CONTAINER FOR SCRAP SUBMERGED IN SAID BATH, AN INSOLUBLE ANODE INSAID BATH DISPOSED BELOW AND SEPARATED FROM THE SCRAP AND THE CONTAINER, SAID ANODE BEING INSULATEDLY MOUNTED IN SAID VESSEL IN A SUBSTANTIALLY HORIZONTAL POSITION WITH RESPECT TO SAID CONTAINER, A CATHODE IN SAID BATH ON THAT SIDE OF THE SCRAP OPPOSITE THE ANODE AND SEPARATED FROM THE ANODE AND FROM THE CONTAINER AND SCRAP, SAID SCRAP BEING THUS POSITIONABLE INTERMEDIATE THE ANODE AND CATHODE SO AS TO INTERCEPT ANODIC OXYGEN GENERATED AT THE ANODE AND TO FUNCTION AS A BIPOLAR ELECTRODE, CURRENT MEANS FOR CONNECTING THE ANODE 